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THE ANNALS OF „DUNAREA DE JOS” UNIVERSITY OF GALATI
FASCICLE XIV MECHANICAL ENGINEERING, ISSN 1224-5615
2009
61
SPECIFIC ASPECTS OF MODELLING AND
DESIGNING GEAR PUMPS
Assoc. ec. dr. eng. Adrian Mihai GOANTA
University “Dunarea de Jos” of Galati,
Research Center for Mechanics of the Machines
and Technological Equipments
ABSTRACT
The paper intends to highlight, in the context of general geometrical modelling, the
specific aspects of design and modelling of a gear pump. In practice in such
situations containing toothed gear it is recommended to use specific subroutines
that are able to access library data bases.
KEYWORDS: CAD/CAE, Autodesk Mechanical Desktop 2008
1. Introduction CAD - Computer Aided Design is now
increasingly used in the various fields of mechanical
engineering, architecture or product design, being a
rapidly developing field. The modern design
assistance is no longer limited only to the systems
simple drawings using the computer, followed by
placement of sizes and shades, but have evolved by
adding features and new instruments for 3D
modelling, with the possibility of creating solid
models and geometric surfaces, based on the
parameters specified by the design engineer.
The design is an iterative process and
consists of several phases, some wider, some more
diminished. These phases are:
� Comparative study –allows to identify the shortcomings of the already designed products
and it is carried out by an experienced engineer
that concludes whether launching a new
product is convenient
� Defining functions refer to determining both the main function and the secondary ones the
and grouping them into a specification of the
product to be designed. Specification includes
the physical and functional features , cost,
quantity and operating performance
� Synthesis and analysis are relatively interlinked and are contained into an iterative process. A
particular component of a comprehensive
system is conceived by the designer, analyzed,
and improved through analysis and redesign.
This process is repeated until the project is
optimized under the constraints imposed by the
designer. Components and subsystems are
summarized in the global system in a similar
way
� Evaluation refers to the degree of meeting the conditions set out in the specification established in
the problem definition phase. This assessment
often requires the manufacture and testing of a
prototype model to obtain data on performance,
quality and profitability;
� Presentation is the final phase of the project and includes the necessary documentation,
namely the project execution drawings, specifications
of materials, parts lists, etc..
With this type of pump and engines the
transmission of pressurized fluid between suction
and discharge is performed by the gaps between the
pin teeth, the housing and side covers, the fluid
circulation in the pump, between suction and
discharge taking place as shown by the arrows in
Figure 1.
Aspiration is determined by the depression that
arises at the gear teeth outlet in the suction area, fluid
is discharged at the gear teeth inlet in area R. The
efficiency of transport is influenced by the radial
clearance between the teeth and the outer housing, as
well as by the axial clearance on the front surface
between gears and side covers. Transmission is
provided by the upper pins, which, through the gear,
causes the bottom gear to move as well.
Due to the existence of two zones with
different pressures, low pressure suction A and high
pressure discharge R, a strong imbalance of forces in
the static pump (and engine) occurs the resultant
being directed from R to A
FASCICLE XIV THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
62
Figure 1. Sketch of the external oil gear : 1- leading
gear ; 2-led gear ; 3-lathing ; A-suction space; R-
discharge space
2. Theoretical Aspects of Mechanical
Desktop Design Three-dimensional modelling of the oil
pump from Dacia 1310 underlines the benefits of 3D
design using one of the most used software packages
produced by Autodesk Inc. namely: Autodesk
Mechanical Desktop 2008. Assembly generating
starts from the creation of each item of the pump,
namely: pins, lower body containing pin box and oil
propulsion groove/channel , the upper body or sieve ,
shaft, arch and ball, holding screws, nuts and the
sieve which draws the oil from the bath oil.
Parameterization of each item is based on
the working plan "Work features / Work Plan" in
the "Part Modelling menu , drawing the profile
sketch, add profile to the work plan, applying the
constraints and sizing the profile by introducing the
actual dimensions. Perhaps the biggest advantage of
parameterized modelling is to save precious time to
generate views and sections. Thus, for the three
projections of a particular item, open the "Drawing
layout, select the" Multi-views”, then choose the type
of view you want to do , select the plan from which
we look, return to format layout and using the
mouse position the 3 projections, and the axonometric
view . Autodesk Mechanical Desktop 2008 includes
tools for sizing pieces (which can be parameterized
and defining a size can be done by equation) and also
for the drawing annotations, tables etc. for holes, all
these being changed automatically according to
changes made in the part geometry.
Automatic generation of design and
execution and bidirectional association along with the
3D model is one of the most important features of the
software used. Projections are generated in "Paper
Space" and can be of the following types: base,
orthographic, isometric, auxiliary, partially sectional,
full sectional, sectional offset, iso-sectional, detail,
user-defined.
Any change in the three-dimensional model
will be reflected in the design and execution, as any
change of size will lead to changes in the model
3. Generating Gears Teeth The gear teeth can be generated by the
following two methods:
- Manual method, which involves defining an involutes arc with the size resulted from an
engineering calculation, corresponding to the
tooth flank, an arc which multiplied polar around
an axis of rotation and completed with circle arcs
delimiting the head and foot of the tooth lead to
a final sketch of the front tooth, by extrusion this
further generating the 3D model of the gear.
Mention must be made that this method is
recommended for experts in designing and
generation, who master very well the technique
of engineering calculation and subroutines
AutoLISP for the generation of involutes type
curves.
Figure 2. Launching command “Shaft Generator”
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI FASCICLE XIV
63
Figure 3. “Shaft Generator” Window
Figure 4. Gear generating parameter window
- Automatic method of generating gears by command "Shaft Generator" from "Content 3D"
menu - as shown in Figure 2, which involves
opening a generating window title " 3D Shaft
Generator " - Figure 3 where option "Gear"
generation” will be chosen.
Figure 5. Toothed gear obtained by “Shaft Generator”
This option will open a new window shown
in Figure 4, where the designer must define all the
numerical values of the requested geometric
parameters. The result of the gear generation
subroutine is presented in Figure 5.
Figure 6. Leading shaft
Similarly, the pair of toothed gear was made,
having the role of a leading wheel. It should be noted
that it must be keep in mind that both toothed gears
have the same module and their external diameter
should be taken as a parameter in the pump body
design draft/sketch, for the cell generation where the
pair wheels would spin. Also in case of the leading
gear , by means of command "Shaft Generator" it
FASCICLE XIV THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI
64
was generated the cylindrical portion of the rod and
the groove at the rod end which takes the rotation
torque. The groove library contains both grooves as
such and various profiles, standardized or not, that
can be used by the designer to complete the end of a
shaft.
4. Generating the Toothed Gear Pump
After the two toothed gears were modelled, each item
can be modelled and in the end the related model can
be generated taking into account the 3D restrictions of
the adjoining pieces. For a better visualization, in
Figure 7 there were assigned glass properties to those
components that cover the gear. It should be noted
that the items of body and cover types are
characterized by a remarkable complexity of
geometric forms.
Figura 7. Model related to the gear pump assembly
5. Conclusions After completion of the design process, it is
important to transmit accurately the design parts
information to the teams responsible to order and
manufacture the product. If a general software design
is used, this operation often involves the manual
creation of tables and lists of materials (BOMs). Even
in the case of the smallest changes in design, the
manual methods can introduce critical errors that
could lead to delays in its delivery to the customer.
To prevent errors and costly delays, Autodesk
Mechanical Desktop 2008 offers the possibility of
making up a list of materials (BOM) integrated into
normal work flow so that the component table and the
BOM contain information on the component parts,
the whole information being updated as soon as a
change in design is made. These accurate data allow
designers to work more effectively with other
departments and suppliers.
References [1] Axinti, A.S., Nastac, S. * * * Introduction to Hydraulic and
Pneumatic Drives Theory – Impuls Publishing House, 2006,
BUCURESTI; ISBN (10) 973-8132-58-4; ISBN (13) 978-973-
8132-58-0; [2] Axinti, G., Axinti, A.S. Drives of hydraulic and pneumatic –
Dynamically of the equipments and of the systems – vol. II.
Tehnica-Info Publishing House, Chişinău-2008, ISBN-978-9975-910-85-9.
[3] Axinti, G., Axinti, A.S. The theory drives of hydraulic and
pneumatic – Components and systems, functions and features - vol
I. – Tehnica-Info Publishing House, Chişinău-2008, ISBN-978-9975-63-112-9;
[4] Goanţă, A. M. & Axinti A., Geometry stage 3D modelling of a heat station pump. Annals of “Dunarea de Jos” University
of Galati, Fascicle XIV, Mechanical Engineering, 2007, ISSN
1224-5615. pp. 48-51.
[5] Haraga G., Applications of CAD systems Proceedings of
The 3rd International Conference on Engineering Graphics and
Design, June 12-13, Cluj-Napoca, Romania pp.291-294.